The present invention relates to an interchangeable objective provided with a diaphragm-operating ring which is rotatable between a rotatable range for diaphragm preset and a position for automatic diaphragm regulation and, more particularly, to a rotation control mechanism for the diaphragm-operating ring used for changeover between said rotatable range for diaphragm preset and said position for automatic diaphragm regulation.
A photographic camera of automatic exposure control type conventionally has a diaghragm priority mode in which a diaphragm value is preset by the user and a shutter speed for appropriate exposure is automatically regulated in the camera body, a shutter speed priority mode in which, inversely, a shutter speed is manually preset by the user and a lens aperture for appropriate exposure is automatically regulated, and a programmed mode in which a combination of diaphragm value and shutter speed is automatically regulated for appropriate exposure.
Interchangeable objectives used with a photographic camera adopting said three modes of automatic exposure control function or different exposure control functions must include a diaphragm-operating ring provided with a rotatable range for manually presetting the diaphragm value (referred to hereinafter as M-range), in said diaphragm priority mode and a position for automatic diaphragm regulation (referred to hereinafter as A-position) in said shutter speed priority mode and said programmed mode. Information as to whether the diaphragm-operating ring occupies the M-range or the A-position must be transferred to the camera body because different exposure control mechanisms are activated in these two cases.
Any unintentional changeover between the M-range and the A-position must be reliably prevented and, in consequence, a suitable changeover locking mechanism and unlocking mechanism are required. However, the structure for connection between the lens barrel and the camera body has made it difficult to obtain a large rotation angle for changeover between the end of the M-range and the A-position. This has given rise to various problems with respect not only to the strength but also to the degree of freedom for their design. Particularly in an objective of a relatively large diameter, the rotation angle within the M-range must be large but the rotation angle of a diaphragm information transferring lever which is rotatable together with the diaphragm-operating ring is restricted by the claw angle of the mount ring, so that the strength of the changeover locking mechanism may be compromised.